Method and system for positioning mobile units based on angle measurements

ABSTRACT

A method and system for positioning mobile units using angle measurements taken by neighboring mobile units is disclosed. A selected mobile unit and mobile units in the vicinity of the selected mobile unit are selectively instructed to measure and report information related to the position of the selected mobile unit. The reported information is used to compute a position of the selected mobile unit.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/818,602, filed Jun. 15, 2007, which in turn is a continuation of U.S.patent application Ser. No. 11/202,560, filed Aug. 12, 2005, now U.S.Pat. No. 7,233,287, which in turn is a continuation of U.S. patentapplication Ser. No. 10/806,701, filed on Mar. 23, 2004, now U.S. Pat.No. 6,933,890, which in turn is a continuation of U.S. patentapplication Ser. No. 10/308,476, filed Dec. 3, 2002, now U.S. Pat. No.6,768,459, which in turn claims priority from U.S. ProvisionalApplication No. 60/399,782 filed Jul. 31, 2002, which is incorporated byreference as if fully set forth.

BACKGROUND

The invention relates to mobile radio-communication systems and moreparticularly to the positioning of mobile units.

In prior art systems, base stations are equipped with smart antennas.Currently, the most advanced smart antenna is an adaptive antenna whichmay also be referred to as an adaptive array antenna. Adaptive arrayantennas facilitate the measuring of a direction of a of an incomingsignal. Such antennas also enable the device to which they are connectedto control the direction in which signals are transmitted therebyoptimizing the power required for signal transmission.

Adaptive array antennas are often used to obtain positioning informationregarding the location of mobile units. Multipath, however, between amobile unit and a base station often results in inaccurate positioningof mobile units. Where multipath is present, either at the mobile unitor the base station or both, accurate positioning of mobile units isoften difficult or impossible to measure.

It would therefore be desirable to accurately position mobile unitsdespite the presence of multipath and to more accurately position mobileunits where multipath is not present.

SUMMARY

The invention is a method and system for positioning mobile units usingangle measurements taken by neighboring mobile units. A selected mobileunit and mobile units in the vicinity of the selected mobile unit areselectively instructed to measure and report information related to theposition of the selected mobile unit. The reported information is usedto compute a position of the selected mobile unit.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a system for positioning a mobile unit in accordance with anembodiment of the present invention.

FIG. 2 is a method for positioning a mobile unit in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the present invention, the following assumptions are made.Mobile units may be equipped with adaptive antennas wherein the typicaluse of those units make them likely to operate in a known orientation inan elevation plane. The azimutal orientation of the array is not known apriori by the system. When a signal, such as an electromagnetic wave,for example, is incoming from a particular direction, it is possible tomeasure its direction of arrival (with respect to the antenna arrayaxis) with an accuracy of 360/n degrees, where n is the number ofelements of the array.

Further, when the present invention is implemented in a TDD system,there are periods of time where a mobile unit is not transmitting orreceiving anything to/from the base station. Those periods of time areavailable for measuring the signals from other mobiles. Also, where theduplexing method is time-division, the same frequency band is used forboth base-to-mobile and mobile-to-base communication.

Referring now to FIG. 1, typical radio-communication systems want toknow the location of mobile units. In FIG. 1, there is shown a system 10for accurately positioning mobile units. Multipath is shown at themobile unit purely for purposes of describing the invention, as theinvention works equally well where multipath is present at the basestation or at both the mobile unit and the base station. The inventionsimilarly provides increased accuracy when positioning mobile unitswhere multipath is not present. The system 10 comprises a radio networkcontroller 12, at least one base station 16, and a plurality of mobileunits 18, 20, 22, n. Those skilled in the art will understand that thesystem 10 may comprise additional components as well as any number ofradio network controllers, base stations, and mobile units, as desired.

In FIG. 1, the system 10 wants to determine the location of a particularmobile unit, say mobile unit 20 (i.e. the target mobile unit). Thetarget mobile unit 20 is served by a known base station, say basestation 16, which may or may not be equipped with adaptive antennaarrays. The known base station 16 is used by the system 10 to collectinformation regarding the position of mobile units 18, 20 22, n. Thecollected information is used by the system 10 to compute the locationof the target mobile units 18, 20, 22, n. As those skilled in the artwill understand, all relevant collected information related to thelocation of a particular mobile unit is compiled and used to compute thelocation of the mobile unit. Examples of the types of positioninginformation collected from mobile units are direction of arrival,amplitude, propagation delay, and degree of confidence.

In the situation shown in FIG. 1, however, the target mobile unit 20,despite being equipped with an adaptive antenna, is unable to accuratelyreport a direction of arrival because of multipath caused by buildings24, 26. Base station 16, in addition to serving the target mobile unit20, also serves mobile units 18, 22, n. Therefore, where a mobile unit20 cannot accurately report direction of arrival information because ofmultipath at the mobile unit 20, the requesting base station, or both,the system 10 can employ neighboring mobile units 18, 22, n. Theneighboring mobile units 18, 22, n are instructed to measure and reportinformation related to the target mobile unit's 20 position so that theradio network controller (RNC) 12, for example, may compute the targetmobile unit's 20 position despite the target mobile unit's 20 inabilityto report accurate direction of arrival information.

The use of neighboring mobile units 18, 22, n may be triggered by eithera target mobile unit 20 or a base station 16. For example, when thetarget mobile unit 20 is unable to measure a direction of arrival of asignal from a particular base station 16, the target mobile unit 20 maysend an indication to the base station 16 instructing it to employneighboring mobile units 18, 22, n to obtain positioning informationconcerning the target mobile unit 20. Similarly, the base station 16 maysend periodic signals to all mobile units associated with base station16 requesting direction of arrival measurements, or any type ofpositioning information. Where any one of those target mobile unitsfails to properly respond to the request, the system will employneighboring mobile units 18, 22, n in order to position the targetmobile unit 20 which fails to properly respond.

Neighboring mobile units 18, 22, n are preferably in the vicinity of thetarget mobile unit 20 in positions that are known by the system 10.Selecting neighboring mobile units 18, 22, n whose positions are knownprovides an accurate reference point by which to position target mobileunit 20. That is, generally speaking, in situations where positioninginformation provided by a target mobile unit 20 may be inaccurate orsubject to confirmation, that target mobile unit 20 is not able to beaccurately positioned. This is typically the result of an inability of atarget mobile unit 20 to measure received signals as a result of, forexample, multipath. This is the case in the example shown in FIG. 1. Toovercome such situations, neighboring mobile units 18, 22, n whosepositions are known may, in effect, each act as a second base stationthereby providing a plurality of known reference points that may be usedin conjunction with base station 16 to accurately position target mobileunit 20.

To employ neighboring mobile units 18, 22, n to provide positioninginformation for the target mobile unit 20, the system 10 orders eachneighboring mobile unit 18, 22, n to provide an angle measurement (θ)which allows the system 10 to more accurately compute an estimate of theposition of the target mobile unit 20. Each reported angle measurement(θ) is compiled by the system 10 and is available for use in computingthe position of the target mobile unit 20. To order the neighboringmobile units 18, 22, n to provide an angle measurement (θ) for thetarget mobile unit 20, the system 10 instructs each neighboring mobileunit 18, 22, n to separately measure a direction of arrival of a signal28 _(b-m) from the base station 16 and a direction of arrival of asignal 28 _(m-m) from the target mobile unit 20.

In situations where an extremely high number of neighboring mobile unitswith known positions are in the vicinity of a target mobile unit, theneighboring mobile units employed to provide positioning information maybe reduced. For example, where cells are sectorized, the system 10 mayselect neighboring mobile units that are in the same sector of thetarget mobile unit. In addition to reducing the amount of data thatneeds to be calculated, employing only those neighboring mobile units inthe same sector as the target mobile unit increases the number of anglemeasurements (θ) that will be properly reported to the system.Sectorized cells are simply provided as an example, as those skilled inthe art realize that base stations have many ways with which to selectand identify particular mobile units for performing particularfunctions.

Signals 28 _(b-m) and 28 _(m-m) may be characterized by a code, a timeperiod, (i.e. a time slot), and a frequency, as desired. The signalcharacteristics are sent by the system 10 to the neighboring mobileunits 18, 22, n and, if desired, a target mobile unit 20, so that theymay identify which signals should be measured. Once both directions ofarrival are measured, the angle measurement (θ) between the two signalsis measured and reported to the system 10 for processing. In addition tothe angle measurement (θ), the neighboring mobile units 18, 22, n mayeach measure and report the amplitude of the measured signals (i.e. formobile unit 20, signals 28 _(b-m) and 28 _(m-m)) as well as a degree ofconfidence in the angle measurement (θ). The amplitude, for example, maybe used by the RNC 12 to independently calculate a measure ofreliability (i.e. confidence) of the reported angle measurement (θ) todouble check the degree of confidence reported by a particular mobileunit. Of course, if desired, the actual directions of arrival asmeasured by neighboring mobile units 18, 22, n may also be reported tothe system 10.

To instruct each neighboring mobile unit 18, 22, n to measure and reportthe directions of arrival mentioned above, the system sends out messagesto the neighboring mobile units 18, 22, n, as desired. For purposes ofdescribing the invention, two separate messages are used (i.e. a firstand second message), but the messages obviously may be combined into onemessage or similarly may be further divided. The message(s) may alsocontain instructions related to measuring and reporting propagationdelay, amplitude, and degree of confidence. The first message orders theneighboring mobile units 18, 22, n, which are equipped with adaptiveantennas to measure a direction of arrival of signal 28 _(m-m) from thetarget mobile unit 20 for a predetermined duration. The second messageorders the neighboring mobile units 18, 22, n to measure a direction ofarrival of signal 28 _(b-m) from a base station 16 so as to provide areference for the angle measurement (θ) taken between the two measuredsignals, 28 _(m-m) and 28 _(b-m). The base station 16 may be any basestation in the system 10 as determined by the RNC 12. Once theneighboring mobile units 18, 22, n have performed the measurements onsignals 28 _(m-m) and 28 _(b-m), the angle measurement (θ), as well asany other information requested by the system 10, is reported.

It should be noted that mobile units served by base stations other thanbase station 16 may be used in the manner described above to collectadditional angle measurements (θ), as desired, regarding a particulartarget mobile unit. That is, although a single base station 16 is shownin FIG. 1, any number of base stations within system 10 may be used tocollect angle measurements (θ) for a particular target mobile unit. Forexample, assume that neighboring mobile unit 22 has a clear line ofsight to the target mobile unit 20, but not a clear line of sight tobase station 16. In that case, instead of measuring signal 28 _(b-m),mobile unit 22 may measure a signal from any other base station fromwhich it may receive signals and to which it has a clear line of sight.If, in this situation, there are no other base stations from which asignal may be measured, mobile unit 22 would be forced to use theobstructed signal from base station 16. The fact that the signal wasobstructed will be reflected not only in the reported amplitude for thatsignal, but also the reported degree of confidence, as further explainedbelow.

It should also be noted that additional angle measurements (θ) may bemeasured for additional target mobile units as well. That is, anglemeasurements (θ) may be simultaneously collected for more than onetarget mobile unit, as desired.

Once a sufficient amount of reported angle measurements (θ) have beenreceived for a particular target mobile unit 20, the system 10 compoundsall of the measurements and computes the target mobile unit's position.To calculate a degree of confidence in the computed position, the system10 may, for example, calculate the number of properly reported anglemeasurements (θ). The higher the number of properly reported anglemeasurements (θ), the higher the degree of confidence. It should benoted that the required amount of reported angle measurements (θ) andthe required level of confidence, are completely adjustable parametersthat may be set as desired. Although the measurements from mostneighboring mobile units 18, 22, n may be inaccurate, the large numberof them make it likely that at least one of them will be in a goodlocation with respect to a target mobile unit, allowing a significantimprovement in the positioning accuracy in situations where severemultipath exists between a target mobile unit 20 and its serving basestation 16.

To illustrate an example of how the system 10 may be implemented,reference is again made to FIG. 1. In FIG. 1, the target mobile unit 20is locally surrounded by buildings 24, 26 and cannot obtain an accuratemeasurement of the direction of arrival between it and its serving basestation 16, or to any other base station, because of multipath. Mobileunit 22, however, which is not subject to heavy multipath at itslocation, happens to be in clear view of both the target mobile unit 20and the serving base station 16. Mobile unit 22 can therefore report anangle measurement (θ) between the target mobile unit 20 and the basestation 16 and increase the accuracy of the positioning of the targetmobile unit 20. The reported information related to the target mobileunit 20 may involve several other measurements such as those reported byneighboring mobile units 18 and n, all of which are evaluated by system10. Pursuant to the present invention, even if multipath exists in thevicinity of base station 16 which makes it receive signals from mobileunits from all directions, the measurement provided by neighboringmobile unit 22 will still be accurate since the angle measurement (θ)information is measured from mobile unit 22 and not base station 16.

In addition to the system 10 calculating a degree of confidence in acomputed position, neighboring mobile units 18, 22, n may also be ableto provide a degree of confidence with respect to the individual anglemeasurements (θ) that they provide. For example, neighboring mobileunits who were able to properly measure a direction of arrival from thetarget mobile 20 and the base station 16 (see neighboring mobile unit 22in FIG. 1), may transmit a signal indicative of that to the system 10.When the system 10 receives such a signal from a neighboring mobileunit, the system will know that the neighboring mobile unit is providingan angle measurement (θ) with good confidence. Alternatively, where aneighboring mobile unit is unable to properly measure one or moredirections of arrival, the neighboring mobile unit may transmit a signalindicative of that to the system 10. When the system 10 receives such asignal from a neighboring mobile unit, the system 10 will know that theneighboring mobile unit is providing an angle measurement (θ) withoutgood confidence. In this case, the system 10 may be adapted to onlyconsider angle measurements (θ) that are reported with good confidencewhen calculating a degree of confidence for a computed position. Thisallows the degree of confidence for a computed position to beproportional to the number of angle measurements (θ) reported with goodconfidence for the computed position.

It is important to note that the reported information may also includeinformation reported by the target mobile unit 20 itself. For example,the system 10 may utilize the propagation delay reported by the targetmobile unit 20 in conjunction with angle measurement (θ), as reported bymobile unit 22, to compute the position of target mobile unit 20. Inpractice, however, even where an angle measurement (θ) is reported withgood confidence, as with mobile unit 22, the actual angle measurement(θ) used by the system 10 to compute a target mobile unit's position maybe a compilation of many reported angle measurements (θ).

Referring now to FIG. 2, there is shown a method 50 for positioning amobile unit in accordance with an embodiment of the present invention.It should be noted that the method 50 may be used to obtain accuratepositioning information on a particular mobile unit where that mobileunit is incapable of providing accurate positioning information.Similarly, the method may be used to simply confirm or double check, orsupplement positioning information provided by a particular mobile unitin order to increase the probability of accurately positioning mobileunits.

To begin, a target mobile unit is identified in step 52. By targeting aparticular mobile unit, the method 50 is indicating that the position ofthe targeted mobile unit will be computed. The position of a targetedmobile unit may be desired for a wide variety of reasons. Positioning ofmobile units is particularly important for providing various “locationbased” services commonly provided over wireless networks such asemergency 911 services, roadside assistance (included providing userswith driving directions) and providing users with information aboutrestaurants, hotels, banks, etc. in their vicinity. Positioning ofmobile units may also be used by law enforcement purposes, for example,wherein criminal suspects or missing persons may be tracked bypositioning their mobile unit.

Once a target mobile unit is identified for positioning, the methodcontinues in step 54 by sending a signal from a base station to theidentified mobile unit instructing it to send out a signal. (Note, thisstep may be bypassed where the target mobile unit is alreadytransmitting or otherwise sending out a signal.) In step 56, mobileunits within a predetermined geographic area of the target mobile unitare identified (i.e. neighboring mobile units). The neighboring mobileunits are typically mobile units whose positions are known by the systemand are in the vicinity of the target mobile unit. Such neighboringmobile units may, therefore, receive signals sent from the target mobileunit and provide an accurate reference point for computing the positionof the target mobile unit. The position of neighboring mobile units iseasily obtained as neighboring mobile units are typically identified assuch, at least in part, because they clearly receive signals from thetarget mobile unit and at least one base station. As such, they are in aposition to clearly measure directions of arrival from two base stationsthereby allowing a system to accurately compute their position. Ofcourse, the degree of accuracy with which a neighboring mobile unit ispositioned may be reflected in the overall degree of confidence of anypositioning information provided by that mobile unit.

In step 58, the neighboring mobile units are instructed to measure adirection of arrival for the signal sent out by the target mobile unit.Similarly, in step 60, the neighboring mobile units are instructed tomeasure a direction of arrival for the signal sent out by eachneighboring mobile units' respective base station. The direction ofarrival of the signal from the base station acts as a reference formeasuring an angle (θ) between the two signals.

The respective base stations may or may not include the base stationcurrently serving the target mobile unit. That is, there is no limit tothe number of neighboring mobile units used to obtain positioninginformation regarding the target mobile unit. Therefore, it is quiteforeseeable that some of the neighboring mobile units may be served bydifferent base stations, with respect to each other and with respect tothe target mobile unit. The number of base stations involved inobtaining information pertaining to a target mobile unit is proportionalto the number of the neighboring mobile units instructed to provideinformation concerning the location of the target mobile unit.

Once directions of arrival have been calculated by the neighboringmobile units, each mobile unit measures and reports angle measurement(θ) between the two directions of arrival in step 62. In addition to theactual angle measurement (θ), each mobile unit may report the amplitudeof the signals for which the directions of arrival were calculated aswell as a degree of confidence in the reported angle measurement (θ). Instep 64, the system compounds all of the reported information andcomputes a position for the target mobile unit, which may be used asdesired. As known by those skilled in the art, the reported informationmay include any information related to the position of a mobile unit, asdesired, and may be requested from not only the neighboring mobileunits, but also from the target mobile unit itself.

Although particular processing functions have been described as beingperformed by particular components, it should be understood thatperformance of processing functions may be distributed among networkcomponents as desired. For example, the processing functions describedas being performed at the RNC may be performed at the base station.

Although the present invention has been described in detail, it is to beunderstood that the invention is not limited thereto, and that variouschanges can be made therein without departing from the spirit and scopeof the invention, which is defined by the attached claims.

1. A base station for positioning a mobile unit comprising: a receiverconfigured to receive an identity of a target mobile unit; a processorconfigured to identify one or more mobile units for reportinginformation related to the position of the target mobile unit, and tocompute an estimate of the position of the target mobile unit using theinformation reported by the one or more mobile units; and a transmitterconfigured to transmit instructions to the identified one or more mobileunits to measure and report information related to the position of thetarget mobile unit.
 2. The method of claim 1, wherein the reportedinformation includes a direction of arrival of a signal received fromthe target mobile unit and a direction of arrival of a signal receivedfrom the base station.
 3. The method of claim 2, wherein the reportedinformation includes an angle between the signal received from thetarget mobile unit and the signal received from the base station.
 4. Themethod of claim 1, wherein the reported information includes an anglebetween a signal received from the target mobile unit and a signalreceived from the base station.
 5. The method of claim 1, wherein thereported information includes an amplitude for a signal received fromthe target mobile unit and a signal received from the base station. 6.The method of claim 1, wherein the reported information includes adegree of confidence for the measured and reported information relatedto the position of the target mobile unit.